Page:NIOSH Manual of Analytical Methods - 5700.pdf/5

 FORMALDEHYDE ON DUST/FIBERS: METHOD 5700, Issue 1, dated 15 August 1994 - Page 5 of 5 Y. T. Gagnon and E.R. Kennedy, NIOSH/DPSE. APPENDIX: PREPARATION AND STANDARDIZATION OF FORMALDEHYDE STOCK SOLUTION (ca. 1 mg/mL) Dilute 2.7 mL 37% aqueous formalin solution to 1 L with distilled, deionized water. This solution is stable for at least three months. Standardize by placing 5.0 mL of freshly prepared 1.13 M sodium sulfite solution in a 50-mL beaker and stir magnetically. Adjust pH to between 8.5 and 10 with base or acid. Record the pH. Add 10.0 mL formaldehyde stock solution. The pH should now be greater than 11. Titrate the solution back to its original pH with 0.02 N sulfuric acid (1 mL acid = 0.600 mg formaldehyde; about 17 mL acid needed). If the endpoint pH is overrun, back-titrate to the endpoint with 0.01 N sodium hydroxide. Calculate the concentration, C s (mg/mL), of the formaldehyde stock solution:

where: 30.0 = 30.0 g/equivalent of formaldehyde Na = normality of sulfuric acid (0.02 N) Va = volume of sulfuric acid (mL) used for titration Nb = normality of NaOH (0.01 N) Vb = volume of NaOH (mL) used for back-titration Vs = volume of formaldehyde stock solution (10.0 mL) ALTERNATE ANALYSIS PROCEDURE FOR THE DETERMINATION OF FORMALDEHYDE LIBERATED FROM DUST/FIBER SAMPLES Note: This analysis procedure should only be used where interferences to the chromotropic acid analysis are not present. These interferences include phenol, oxidizable organic material, other aldehydes and alcohols. For formaldehyde determination by the chromotropic acid method, a 4-mL aliquot of the solution resulting from the desorption and incubation of the filter (step 8.) was analyzed by the procedure described in NIOSH Method 3500.[2] The amount of chromotropic acid added to the sample could react with a maximum of 42 µg of formaldehyde per sample aliquot. (Whenever the amount of formaldehyde approached 30 µg per aliquot, the sample was diluted and reanalyzed.) The absorbance of samples at 580 nm was then compared to a calibration curve constructed from results obtained from analysis of calibration standards containing known amounts of formaldehyde. The amount of formaldehyde present in each sample was determined based on the calibration curve. Calibration standards were prepared by dilution of a standard solution of formalin in distilled water (1 mg/mL) and analyzed in the same manner as the samples. The calibration range usually covered 1 to 25 µg of formaldehyde/4-mL aliquot. A limit of detection of 0.44 µg formaldehyde/filter sampler was determined in laboratory evaluation of this analysis procedure.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94